The decarbonization of gas turbine power plants is essential in the energy transition

particularly in countries such as Indonesia

where gas turbines play a critical role in supporting the intermittency of renewable energy sources. This study presents a numerical investigation of hydrogen-natural gas co-firing in an F4-class gas turbine combustor using a three-dimensional model reconstructed from high-resolution scanning data. Simulations were performed with hydrogen mass fractions ranging from 0% to 20%

while maintaining a constant turbine inlet temperature to evaluate changes in combustion behavior

emissions

and economic performance. The results show that increasing hydrogen content modifies the flame structure and alters the outlet velocity distribution due to changes in air-fuel ratio. Carbon dioxide emissions decrease by up to 36%

while nitrogen oxide emissions increase by 41%

reflecting the higher reactivity and flame temperature of hydrogen combustion. From an economic perspective

hydrogen utilization increases fuel cost by up to 1.65 times compared to natural gas operation. However

the inclusion of carbon credit mechanisms reduces this increase to 1.50 times. These findings demonstrate the technical feasibility and economic implications of hydrogen co-firing as a transitional strategy for decarbonizing gas turbine systems.